Vehicular repeater systems allow high power mobile radio units to be used in extending the communication range of portable radio communication units. In operation, a vehicular repeater receives communication signals from a portable radio and retransmits these signals at a higher power to enable extended range communication. Preferably, such range extension is automated such that when a portable radio is within communication range of a vehicular repeater this range extension takes place. A problem of interference may develop when multiple vehicular repeaters within communication range of the portable radio attempt to retransmit the communication signal. The prior art addresses this problem by providing a management scheme that designates one of the vehicular repeaters to be a priority repeater, which priority repeater has primary responsibility for repeating signals of any portable radio within communication range. One such priority scheme is described in U.S. Pat. No. 4,056,779 issued to Toler on Apr. 5, 1976 for a Vehicular Repeater. In this implementation, each vehicular repeater entering a particular communication environment determines whether or not to assume priority repeater status by monitoring for repeater communication. If none is detected, the vehicular repeater assumes priority repeater status and transmits a communication signal to update the status of any other vehicular repeater operating in that environment. Thus, only one vehicular repeater operates as a priority repeater in the particular communication environment.
In a typical prior art implementation, a priority vehicular repeater system receives transmission from a portable radio on a particular channel and retransmits the signal using a high power mobile radio on another communication channel. Non-priority vehicular repeaters monitor both communication signals to determine whether signals transmitted by the portable radio are being properly re-transmitted by the mobile radio at the priority repeater. If it is determined that transmissions from the portable radio are not being retransmitted, each non-priority repeater monitoring the situation updates its delay counter until one of the non-priority repeater has a delay state of zero, and therefore assumes priority repeater status. Thus, the designation of one of the vehicular repeater as a priority repeater is automatically maintained.
A problem arises when a short burst communication signal, such as an emergency alarm, is transmitted by the portable radio but not retransmitted by the priority vehicular repeater. Under the prior art prioritization scheme based on delay states, a non-priority vehicular repeater will assume priority status after a particular time lapse without retransmission from the priority repeater. However, retransmission of the signals from the portable radio will not occur until after this time lapse. Thus, the emergency alarm or other short data burst signal could be transmitted by the portable unit but not retransmitted by any vehicular repeater because the original priority repeater was unavailable. This break down of protocol occurs despite the detection of the communication signal containing the emergency alarm by non-priority vehicular repeaters.
While the use of delay states offers a straight forward implementation and works in a substantial number of operating environments, the inability to support the repeating of short burst communication signals, such as emergency alarm signals, when a priority repeater is no longer available is a problem in the art. It is desirable to take advantage of the benefits offered by a vehicular repeater system with automatic transmission priority scheme, while providing support for such short burst communication signals. Therefore, an improved vehicular repeater system with automatic priority assignment is needed.